1. Field of the Invention
This invention relates to a microgap type surge absorber, and more particularly to a microgap type surge absorber having an improved durability to repeated surge applications or a large current surge application.
2. Description of the Related Art
Surge absorbers are used to protect devices connected to communication lines, such as, telephone lines, telecopier lines, and the like, from electrical surges.
FIG. 4 shows a conventional surge absorber comprising a columnar or rod-shaped insulator element 1, the surface of which is coated with a conductive material having a microgap 2 in the coating of the center of the element 1, cap electrodes 3a and 3b at each end of the element 1, each having a lead wire attached thereto. The entire assembly is encased in a sealed glass tube 5 which is charged with an inert gas 4, except that the distal portion of the lead wires extend exterior of the glass tube to provide electrical connection means.
When a voltage above the discharge starting voltage of the microgap is applied to such a conventional surge absorber, a glow discharge immediately starts from near the microgap. This glow discharge is conveyed to both cap electrodes, and then an arc discharge is formed between the cap electrodes through or near the microgap to thereby absorb the applied surge.
If repeated surge applications or a large current surge application is applied to such a conventional surge absorber, the microgap of the surge absorber may be damaged by the heat thereof. Accordingly, a problem with the conventional surge absorber is that the surge absorbing performance is degraded due to the damage to the microgap caused by the repeated arc discharges or the large arc discharge, and its lifetime is shortened.
Japanese Unexamined Published Patent Application Sho 63-205026 discloses such a conventional surge absorber.